Method of making alkali-metal cyanide



June 24 ,.11924 F. J. METZGER METHOD 0F MAK'I'NG ALKALI METAL CYANIDE Filed March 25. 1924 EiVENTOR A ATTORNEYS Patented June 24, 1924.

FLOYD J. METZGER, on NEW YORK. N. Y"

ASSIGNOR TO CALIFORNIA GYANIDE COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION DELAWARE.

METHOD OF MAKING ALKALI-METAL CYANIDE.

Application filed March 2 5, 1924. Serial lN'o. 701,736.

' clear, and exact description of the invention,

such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to'the fixation of nitrogen by heating mixtures of alkali metal compounds and carbon with or without a catalyzing agent in the presence of nitrogen or nitrogenous gases, and particularly to an improved method whereby the production of alkali metal cyanide is assured.

A method of fixing nitrogen is described in United States Letters Patent No. 1,322,- 195 and involves the heating of mixtures of alkali metal carbonates or oxides with car-,

bon and relatively small amounts of iron, preferably in the form of iron oxide. in the presence of nitrogenous gas- As little as two per cent of iron is eil'cctive and small amounts are used preferably so that the capacity of the reaction chamber will not be reduced by the presence of surplus and inactive material. The furnace product consists of alkali metal cyanide combined with other alkali metal compounds and carbon. The cyanide may be recovered by leaching the product with suitable solvents but preferably the product is treat-ed with carbon dioxidc under regulated :onditious to rclease hydrocyanic acid which is condensed as a liquid.

In conducting theprocess a nitrogenous gas containing a relatively high proportion of nitrogen is preferred. In practical operations the nitrogen can be obtained from a liquefaction apparatus but a less expensive and more read ly available source is found in the gases which escape from the heating furnace which is employed to maintain the have invented certain newtemperature of the reaction. The furnace gases are scrubbed to remove carbon diox-' ide therefromand the balance, which is principally nitrogen, is delivered to the re tort in which the cyanide reaction is car-.1 j

ried out. "The nitrogenous'gas, whether derived from a liquefaction apparatus or from furnace gases, usually contains more or less oxygen.

At the high temperatures which are necessary in the reaction zone where the cyanide is formed oxygen has no deleterious effect upon the reaction, particularly in the presence of carbon.- At lower temperatures, that is to say, below substantially a red heat, the oxygen is undesirable since it combines with the cyanide to form a cyanate. The cvanate cannot be separated readily from the cyanide if the product is leached and it is not decomposed by carbon dioxide to producc hydrocyanic acid. It consequently represents a loss of cyanide and reduced ofiiciency of the process regardless of the manner in which the cyanide is recovered from the furnace product.

It is the object of the present invention to rotatcd and which is heated externally by means oi a suitable furnace supplied, for example. with oil burners or other means of generating combustion gases capable of producing a temperature of .from 950 to provide a process of fixing nitrogen which 1100 C. Theportion of the reaction chamher in which the reaction occurs is completely filled with the mixture of carbon and alkali metal compound with or without a'catalyzer such as iron. The complete filling of the reaction chamber ensures ,the proper contact of the nitrogenous gas with the mixture, particularly when the =mass is The rotation of the reaction chamber is conexist. By maintaining the furnace mixture .largely of carbon monoxide and from would cool rapidly tinued during the entire period while the reaction is being carried on and causes the particles to constantly shift their positions, expose fresh surfaces to the action of the gas and prevent channeling' The mixture is heated meanwhile to the temperature of the reaction preferably in the neighborhood of 1100 C. by the heating gases which surround it, the heat being conducted through the walls of the reaction chamber and through the material therein so that all of the material is at substantially the same temperature. The rotation of the reaction chamber ensures uniformity of heating.

The nitrogenous gas is introduced at the lower end of the reaction chamber and proceeds through the mass of material therein to the upper or outlet end where it consists which it is discharged to the atmosphere. At its lower end the reaction chamber extendsfor some distance beyond the wall of the combustion chamber in'order that proper bear: ings for the tube may be maintained. This extension is considerably cooler than that portion of the tube which is within the combustion chamber and if the mixture were permitted to descend into the extension it particularly if the nitrogenous gas were introduced directly at the end of the tube.

This coolingof the furnace mixture 1n the presence of nitrogenous gas has no d1sadvantage if the gas is substantially free from oxygen. On the other hand, the presence of oxygen in contact with the furnace product at low temperatures results in the formation of cyanate. To avoid this difli culty I introduce a plug or plunger into the lower end of the tube and arrange it so that the contents of the tube cannot descend substantially beyond the wall of the combustionchamber. The plunger is provided with passages through which the nitrogenous gas is delivered to the furnace mixture above the plunger and first contacts with the mixture accordingly at atempera; ture at which alkali metal cyanates cannot with which the nitrogenous gas first contacts I always at a temperature above that at which alkali metal cyanate can exist, I avoid the formation of cyanate in the mixture and thus materially ncrease the efficiency of the process. r

In the accompanying drawlng an apparatus which is adapted for use in conducting the prodess is illustrated in longitudinal section. i Referring to the drawing, 5 indicates a furnace eonstru'cted of brick work or other suitable material and preferably having a producer 8 to a passage refractory lining 6 enclosing a combustion chamber 7 a A suitable fuel, in this instance producer gas, may

9 from which the gas is delivered through gas inlets 10 to the combustion chamber 7 where the gas is mixed with air and is burned to produce the necessary high temperature. The combustion products pass over a bridge wall 11 and are "withdrawn from the chamber, preferably passing an economizer (not shown). No surplus heat is employed in preheating the air which is mixed with the gas before combustion thereof. Reference is made to Letters Patent-No. 1,322,195 above referred to for the details of this arrangement.

A tube 12, preferably of oxidation-resistant material such as an alloy containing nickel and chromium, is disposed in suitable openings in the walls of the furnace 5 to cocupy an inclined position. The tube is pro vided with flanges 13 and'il t resting on rollers 15 and 16. The flange? 14 bears against a thrust roll 17 which maintains the tube in proper position in the furnace. The tube may be rotated by means of a chain 18 engaging a sprocket 19 thereon and. a sprocket .20 on a shaft 21 which may be actuated in any suitable manner.

The tube 12 is filled with the furnace mixture from the upper end which is open as indicated in the drawing. The lower end of the tube is preferably closed by a head 22 nitrogenous gas is introduced. The pipe 26 passes through a gland 28 so that the tube 12 may rotate while the pipe 26 remains stationary. The nitrogenous gas is delivered through the passage 25 to the furnace material. The latter cannot descend beyond the lower limit of the heating zone and,consequently cannot cool to a temperature lower than that of the reaction. Thus all of the reacting mass is held at the proper temperature to preclude the formation of cyanate.

At the conclusion of the reaction the head 22 and plunger 23 are removed and a portion of the furnace product is withdrawn, that portion which is held in the preheating zone being permitted to descend into the reaction zone. The plunger and head are replaced and the operation is continued.

Various changes may be made in the details of operation as hereinbefore described without departing from the invention or sacrificing anyof the advantages thereof.

I claim be supplied from a gas The, method of fixing nitrogen, which preventing initial contact of the nitrogenous 1 comprises filling a reaction chamber with a .gas with the mixture at a, temperature submixture, containing an alkali metal comstantia-lly lower than that maintained in the pound and carbom heating the mixture in reaction chamber, thereby avoiding oxida- 5 the reaction chamber to a temperature at tion of the alkali metal cyanide in the mixwhich nitrogen combines therewith to form hire to form cyanate. 15 alkali metal cyanide, passing nitrogenous In testimony whereof I atiix my signature gas containing oxygen from one end of the i reaction chamber through the mixture and FLOYD J. METZGER. 

